Incising is carried out on lumber or timber to form punctures or incisions in the surface to permit penetration of preservatives and the like into the lumber. In today's markets, better penetration of preservatives is required and tests carried out show that in order to obtain a proper penetration of preservatives in certain wood species, close spacing of incisions or penetrations is required on preferably all four surfaces of a piece of wood or timber.
Devices for incising lumber generally include an incision roll for at least one surface. The roll has a series of teeth and a pressure is applied between the roll and the surface of the wood so the teeth penetrate. If the incisions are too close together, it has been found that wood strands, slivers or splinters are stripped from the face of the lumber which not only reduces the grade of the lumber, but also clogs up the teeth of the incising rolls. Comb type or spacer ring cleaning systems are often provided in spaces left between discs having incising teeth on their periphery. One method of preventing slivers from forming has been developed by Silcox and is disclosed in U.S. Pat. No. 4,706,722. This patent describes a lumber incisor with a plurality of incisor discs with teeth on the periphery, mounted on a shaft with a plurality of annular cleaning rings between the incisor discs which freely move and during the incising operation are pushed upwards or downwards depending on the position of the wood relative to the incising roll, thus cleaning wood strands, splinters or slivers caught in the incising teeth. Annular cleaning rings or combs with cleaning teeth between incisor discs require a space between the incisor discs that does not permit a close pattern of incisions to be made with a single roll.
The preservative lateral penetration in one direction from a single incision is in the order of 1 to 2 mm for spruce and lodgepole pine. Thus the spacing between rows of incisions must, therefore, be reduced to less than 3 mm.
The incision density required to treat, for example, spruce heart wood to Canadian standards is over 10,000 incisions per square meter. These incision densities cannot be achieved with a single incisor roll without strands, slivers or splinters being formed resulting in damage to the surface of the wood and also clogging of the incisor roll with the inevitable result of considerable downtime to clean the machine and prevent incisor tooth breakage.
Dual incisors have been provided for incising veneer, however, veneer incision is for a different purpose from that of timber or lumber incision. Veneer incision is provided to expand green veneer or to prevent contraction or warping when the veneer is subsequently formed into plywood and the like. One example of a multiple roll incision arrangement for veneer is disclosed in U.S. Pat. No. 4,655,869 to Tellman et al. While this patent does disclose two rollers in line, it does not suggest that the rolls be synchronized to form a pattern of incisions, and in fact discloses at column 3, line 41, that the sheet may be run through the nip up to four times on each side to achieve a desired expansion. Furthermore, the patent relates to green veneer to cause expansion, thus preventing contraction of the veneer during the drying step.